This invention relates to the field of testing and measuring apparatus. More specifically, it relates to the field of apparatus for measuring the power output of ultrasonic transducers. Although such transducers find wide application in industry, they are particularly useful in the medical field as a diagnostic tool. In that context the transducer produces ultrasonic waves which are projected into the human body. The intensity of the waves must be accurately maintained to insure that no physiological damage is done to the patient. Thus, it is necessary to periodically calibrate transducers and to measure their transmitted acoustic power.
Measurement devices for ultrasonic transducers are known. See, for example, the references discussed in the prior art statement which follows. However, those devices have not been entirely satisfactory in accuracy or in their ability to measure low transducer power output on the order of 300 mircowatts. Typically, such devices employ mechanical balance type schemes with the attendant inaccuracies due to the friction of the fulcrum, the weight of wires, etc., which thereby limit the accuracy of the testing devices. It is accordingly an object of the present invention to provide an improved power measuring apparatus for ultrasonic transducers which has a greater range and sensitivity than prior devices.
Another object of the present invention is to provide a measuring apparatus of the type indicated employing a tautband d'Arsonval meter movement as part of the transducer target suspension.
Another object of the invention is to provide an automatic restoring circuit for maintaining the target at the null point, which circuit provides a direct meter reading of the current required to maintain the null, which reading may be calibrated to correspond to the power output of the transducer.
Other objects and advantages of the invention will be apparent from the remaining portion of the specification.